Ever since I shot a young mule deer through-and-through at 270 yards with a 100-grain softnose from a .243 Winchester-chambered rifle, and he wandered off in a rather unconcerned manner until I shot him again, I’ve mistrusted 6mm calibers for big game.

Given my druthers, I prefer to thump mulies with at least 1,500 foot-pounds of energy, and most 6mms just don’t provide that amount out as far as I sometimes shoot. Granted, that much energy is not necessary–most hunters agree that 1,000 ft-lbs is adequate for deer–but a big, heavy-bodied mule deer buck can soak up a lot of punishment.

So my accurate little .243 got back-burnered into being a coyote rifle. When I did take it deer hunting, I kept shots within 200 yards, or at most 250. I don’t like being hampered, so I didn’t take it very often. But I always had this sneaking little crush on 6mm-diameter projectiles.

Though not commonly seen today, the .240 Weatherby is a fine cartridge that gives hunters as much oomph at 400 yards as the .243 Winchester does at 250.

I figured that if shot fast enough, they’d be a real ticket to low-recoil happiness. I considered cheating on my .243 by purchasing a 6mm Remington. I had a burning desire to own a .243 WSSM until I shot my friend’s, which cured me rather quickly upon fighting difficult extraction and feeding issues. Mostly, I considered building a wildcat in 6mm-06, but just never did.

For whatever reason, even though it’s provided a viable 6mm solution since 1968, I never considered the .240 Weatherby Magnum until last spring.

The .240 SolutionThe .240 Weatherby Magnum was Roy’s last baby. It is built on a case unique to itself: Though it has a case head diameter the same as the .30-06, as well as similar case length, it is a belted case, which means that it’s got a smaller body diameter than the ’06 and can’t be formed out of any other case. Shooters must use factory ammo, reload cases left after firing that factory ammo, or purchase component cases from Weatherby for about two bucks apiece and handload them, and for that reason most economy-minded handloaders don’t like the .240 Weatherby.

Though long shots are always tricky, the use of a reticle such as Zeiss’ Rapid-Z makes holdover much more predictable.

But it has one very important advantage: It leaves all other factory 6mms in the dust, to the tune of about 150 fps over even the fastest ones. Relevance? This means that it packs as much energy at 400 yards as the .243 Win. does at 250. It is a factory-available cartridge, available chambered in factory-produced rifles, that is a capable performer as far as I’d want to shoot at a mule deer.

Factory figures indicate that a 100-grain Nosler Partition exits the muzzle at 3,406 fps, maintaining 1,500 ft-lbs of energy to over 300 yards and 1,000 ft-lbs past 500 yards. Another useful load pushes an 85-grain Barnes TSX to 3,500 fps. The Weatherby catalog lists five different loads in all, covering about every reasonable use that could make a 6mm lover smile.

Real-life performance out of my Mark V Ultra Lightweight rifle runs a bit substandard of those factory figures. The 85-grain TSX load is pretty close, averaging almost 3,400 fps, but the 100-grain Partition load averages almost 200 fps slower than advertised figures. It’s still 250 to 300 fps faster than the same bullet out of the standard .243 Win., and since my rifle likes the Partition load, I’m pretty confident with it out to about 400 yards.

6mm Proof In The PuddingJust last week I spent a couple of days hunting antelope on Wyoming’s plains. The country was surprisingly broken for being wide open and treeless. Casey Tillard–a fifth generation rancher on the Tillard 55 spread–was my host, and as evening stretched our shadows we stalked a good buck with a harem of does herded up in a secluded swale. The wind died with the sun, and I daypacked my rifle and ranged the buck. The LED display in the Zeiss 10X42mm RF binoculars read 357 yards, and the swale reached broad and hollow before us, offering no cover to shield a closer stalk. I reached up and dialed the magnification knob on my scope to 11 2/3 power.

The good folks at Zeiss had loaned me a fantastic Victory Diavari FL scope for the hunt, incorporating the company’s long-range Rapid-Z 800 reticle to complement the range-finding binoculars. It’s an outstanding piece of glass, bright and perfectly clear, and though it’s a bit too rich for my new-father blood price-wise, the company also builds the Rapid-Z reticles into its Conquest line, which is affordable to anyone serious about good optics.

The Rapid-Z is unique in that, coupled with an online ballistic resource, it allows a shooter to input very detailed load data, including handload info and climatic conditions. It then not only calculates specific points of impact relevant to the numbered ballistic hash lines, it has an "optimize power" function that calculates the best match between your scope’s magnification setting and your cartridge’s trajectory. Obviously, as you zoom that power ring in or out, the ballistic hash marks on the reticle span more or less of your downrange target, and by zooming it to a particular setting you can make the span of those hash marks equal your bullet’s drop. For instance, the Victory Diavari scope I had mounted on the .240 Weatherby had a magnification range of 4 to 16X, but the optimum power with the 100-grain Partition at the velocity that particular gun gave was 11.68X. Sure enough, set just a shade past the halfway point between 11 and 12X my shots at distance impacted precisely where I held the corresponding ret
icle mark on the target.

The pronghorn buck fed in a patch of rabbit brush, unaware. In the stillness of the moment before the shot, I looked in vain for wind movement in the grass between myself and the buck and noted the absence of the touch of wind on my skin. The hash mark for 350 yards steadied on the buck’s shoulder, and with a spunky bark the Mark V sent a 100-grain Partition across 357 yards and into the precise spot I aimed at. Entering just behind the large shoulder bone, it exited mid-ribcage on the off side. The buck wobbled a moment or two and dropped.

The .240 Weatherby is not for everyone. It’s only available in Weatherby Mark V rifles, so there’s not really a price-point option for shooters on a budget. As mentioned, until set up with a quantity of brass to reload, it’s not cheap to shoot, either. But it’s an honest 400-yard deer cartridge, and with lighter bullets coughing out at 3,500-ish fps, it’s a heck of a predator round to as far as you can hit ‘em. If you love 6mm-diameter projectiles but have always felt a little undergunned with your .243 Win. or 6mm Rem., I’ll wager a .240 Weatherby Magnum would become the favorite rifle in your gun cabinet.

WARNING: The loads shown here are safe only in the guns for which they were developed. Neither the author nor InterMedia Outdoors, Inc. assumes any liability for accidents or injury resulting from the use or misuse of this data.NOTES: All figures are factory published numbers. Actual velocity will vary depending on your particular rifle.